I used to beat myself up about not remembering details of books, even ones I read only a few months ago. I still try to take notes and revisit those often, but PG's take on this help ed reduced my anxiety about it:
> Reading and experience train your model of the world. And even if you forget the experience or what you read, its effect on your model of the world persists. Your mind is like a compiled program you've lost the source of. It works, but you don't know why.